Question

(a) What are the periods and groups in a periodic table? Give two characteristics of each.  (b) In terms of electronic configurations explain the variation in the size of the atoms of the elements belonging to the same period and same group.  (c) Given alongside is a part of the periodic table. As we move vertically downward from $Li$ to $Fr$ .    (i) What happens to the size of atoms? 
 (ii) What happens to their metallic character? (d) Name two properties of elements whose magnitudes change when going from top to bottom in a group of the periodic table. In what manner do they change? 
(e) Rewrite the following statement after correction, if necessary: 
Groups have elements with consecutive numbers.

$Li$	$Be$
$Na$
$K$
$Rb$
$Cs$
$Fr$	$Ra$

Answer 1

Hint: Periodic table is in a table form in which all the known (discovered) elements are arranged according to their atomic numbers, chemical properties and electronic configuration. The table has seven rows which are known as “periods” and eighteen columns which are known as “groups”. The groups and periods have some characteristic properties, which we will see in detail.

Complete answer:
We will first see the period table:-

(a) The table has horizontal rows which are known as “periods”.
Two characteristics of periods are:-
(i) The consecutive elements present in a period have consecutive atomic numbers.
(ii) The no. of elements in a periodic table is the same as the maximum no. of electrons which can be present in various shells of the periodic table.
The table has vertical columns which are known as “groups”.
Two characteristics of groups are:-
(i) The elements on moving down a group do not have consecutive atomic numbers.
(ii) The elements in a group have similar electron configurations and chemical properties.
(b) In a period, the size of the atom decreases on moving from left to right. As we move from left to right in a period, the atomic number of elements increases and we know that, the no. of protons and electrons in the atom increases. The electronic configuration of atoms increases within the same shell. The effective nuclear charge increases on the electrons and the electrons are pulled closed and hence, the atomic size decreases.
Now, if we talk about a group, then on moving down the group, the atomic size increases. The no. of electron shells in the atoms increases and the electronic configuration also increases due to which the atomic size increases.
(c) As we move vertically down the group from $Li$ to $Fr$ ,
 (i) The atomic size increases due to the addition of a shell.
(ii) The metallic character increases from lithium to francium because the ionization enthalpy decreases.

$Li$	$Be$
$Na$
$K$
$Rb$
$Cs$
$Fr$	$Ra$

(d) The two properties of elements whose magnitudes change when going from top to bottom in a group of the periodic table are atomic size and electronegativity.
Size- On moving down the group, an extra shell is added, so the atomic size increases.
Electronegativity- On moving down the group, as the size increases, the electronegativity decreases due to less effective nuclear charge.
(e) The given statement is wrong, and the correct statement is:
Periods have elements with consecutive numbers.

Note:
As we move down in a group of periodic tables, then, a shell is being added and hence, the atomic size increases. Due to which, the electronegativity and the ionization energy of the atom decreases. Hence, the metallic character of the atom increases and on moving from left to write in a period, electronegativity increases and the metallic character decreases.